Traders said the higher WTI prices were a result of reduced flows from Canada’s Keystone pipeline, which has been operating below capacity since late last year due to a leak, cutting Canadian supplies into the United States.

Outside North America, Brent crude eased on the back of a dip in Asian stocks and a stronger dollar, which potentially curbs demand as it makes fuel more expensive for countries using other currencies domestically.

Brent crude futures were at $65.48 per barrel, down 19 cents, or 0.3 percent, from their last close.

The opposing price direction of the two main crude benchmarks has sharply reduced WTI’s discount to Brent, to around $3.22 per barrel on Tuesday, down from over $7 in late 2017.

Overall, oil markets remain well supported due to supply restraint by the Organization of the Petroleum Exporting Countries (OPEC), which started last year in order to draw down excess global inventories.

“OPEC and Russia continue to support the production cuts that are due to expire at the end of this year, and they assure markets that there will be an orderly ramp up of production once the cuts expire,” said William O’Loughlin, investment analyst at Australia’s Rivkin Securities.

While most of OPEC, especially its de-facto leader Saudi Arabia, is showing strong support for the production restraint, non-OPEC producer Russia has shown signs it may at some stage gradually start to increase output again.

Saudi Arabia – not least in an attempt to give the planned listing of its state-owned oil giant Saudi Aramco – a boost, is keen for Russia and other producers to keep withholding supplies to prop up prices.

But soaring U.S. production is threatening to erode OPEC’s efforts.

Last week, the amount of U.S. oil rigs drilling for new production rose for a fourth straight week to 798, in an indication that U.S. crude output, already at a record 10.27 million bpd, may rise further.

The United States late last year became the world’s second biggest oil producers, only slightly behind Russia and ahead of top exporter Saudi Arabia.